Padronização de uma tarefa de reconhecimento de objetos e discriminação de objetos similares com múltiplas sessões

Abstract

Recognition memory, a subtype of explicit/declarative memory, is the capacity of distinguishing new from familiar stimuli. This ubiquitous type of memory is shared among different species, and recognition might occur through recollection or familiarity. A process underlying recognition is pattern separation, the ability to form unique representations of similar events, providing less confusing memory representation, which can lead to different behavioral outputs. There has been significant effort towards the development of appropriate tasks to evaluate these types of memory in animal models. Considering the need for faster data accumulation, in order to implement electrophysiological recordings, some studies have been devising protocols with multiple tests a day. In this work, we sought to adapt a recognition and object discrimination memory task with multiple sessions. We used 15 Wistar adult rats (3-4 months old) overall, in which 5 rats were used in Experiment 1, 5 rats were used in Experiment 2 and 5 rats were used in Experiment 3. Animals underwent a recognition task and an object discrimination memory task with multiple sessions. The recognition memory task presents 2 sessions, comprising a sample session and a test session. The discrimination task used objects that varied in their similarity, and comprised 4 sessions: a sample session and 3 test sessions, applying a 3-minute intersession interval. The objects were created from LEGO blocks, with different degree of features overlap. In the sample session, rats were exposed to three identical copies of an object, in specific positions of the circular track. The test sessions included 2 equal objects, originally presented in sample sessions, and a similar object that shared 25%, 50% or 75% degree of features overlap. In Experiment 1, rats performed 3 laps around the circular track in each sample and test sessions, up to 10 sessions a day. In Experiment 2, rats performed 1 lap around the circular track in each sample and test sessions, up to 10 sessions a day. In Experiment 3, however, rats performed 2 laps around the circular track in each sample and test sessions, up to 5 sessions a day. Results showed that in Experiment 1 rats consistently presented significant discrimination indexes in the recognition task. In the discrimination task, rats discriminated objects presenting 25% degree of features overlap, but animals could not discriminate objects presenting 50% or 75% degree of features overlap. Both Experiments 2 and 3 provided non-significant results for recognition and discrimination tasks. Therefore, our findings indicate that Experiments 1 offers a promising model for memory evaluations, but we recommend that the protocols explored in Experiment 2 and 3 should be analyzed and improved in future studies, in order to enable electrophysiological recordings.